Film of N Type (100) Oriented Single Crystal Diamond Semiconductor Doped with Phosphorous Atoms, and a Method of Producing the Same

ABSTRACT

There is provided an n type (100) oriented single crystal diamond semiconductor film into which phosphorus atoms have been doped and a method of producing the same. The n type (100) oriented single crystal diamond semiconductor film, characterized in that (100) oriented diamond is epitaxially grown on a substrate under such conditions that; the diamond substrate (100) oriented diamond, a means for chemical vapor deposition provides hydrogen, hydrocarbon and a phosphorus compound in the plasma vapor phase, the ratio of phosphorus atoms to carbon atoms in the plasma vapor phase is no less than 0.1%, and the ratio of carbon atoms to hydrogen atoms is no less than 0.05%, and the method of producing the same.

TECHNICAL FIELD

The film of n type (100) oriented single crystal diamond according to the present invention can be applied to such electric devices as ultraviolet light emitting devices, electron emission sources, high frequency transistors, high power transistors, X ray and particle ray sensors, and X ray and particle position sensors.

The present invention relates to a method of preparing a film of n type (100) oriented single crystal diamond, and provides a manufacturing method according to which an n type (100) oriented diamond semiconductor that can make up such general semiconductor devices as ultraviolet light emitting elements, electron beam emission elements, power semiconductor elements and high frequency semiconductor elements can be formed efficiently.

BACKGROUND ART

Conventional single crystal diamond semiconductor films can be manufactured by the method of generating microwave plasma, and thus growing a diamond film which includes carbon and phosphorus on a heated diamond substrate within a vacuum container into which a gas including hydrogen, carbon and phosphorus atoms has been introduced (Patent Document 1). Here, it is described that “In order to grow a single crystal diamond film, it is desirable to use heteroepitaxially grown diamond or a single crystal diamond substrate. Though any of the (111) plane, the (110) plane or the (100) plane may be used, the (111) plane is desirable,” and according to the document, a film of n type (111) oriented single crystal diamond semiconductor doped with phosphorus atoms is fabricated using the (111) plane of a diamond crystal in an embodiment, and the generation thereof is confirmed. Furthermore, in the disclosed scope of the invention, there is a description that this invention can be practiced in a region where the ratio of the number of atoms for P/C of P in phosphine PH₃ to C of methane CH₄ is such that P/C <4% and the ratio of the number of atoms for C/H of C in CH₄ to H of hydrogen H₂ is such that C/H <1%, and that n type (111) oriented single crystal diamond semiconductor, which are examples for defining the scope of the invention and designated as  in FIG. 1, can be formed. Meanwhile, it is described that in comparative examples designated as × it cannot be obtained on the (111) plane.

Concerning this, the inventors published some information similar to the above (Non-patent Documents 1 and 2).

However, as far as the present inventors know, there are no preceding examples that confirmed the existence of an n type diamond semiconductor on the (100) plane in any patent or academic paper. In addition, there is a reported example that no n type diamond semiconductor grew on the (100) plane under the synthesis conditions on the (111) plane (Non-patent Document 4). As described above, conventional n type diamond semiconductors have been obtained only with a particular ratio of the number of atoms only on the (111) plane. Even when such methods are attempted, however, a film of n type (100) oriented single crystal diamond semiconductor, which is important in the industry, could not be obtained, due to poor reactivity.

There was attempt to manufacture films of (100) oriented single crystal diamond semiconductor which allow provision of an enlarged area and flattening through polishing relatively easily, and low interface state density, which are suitable for semiconductor devices, compared with diamond substrates having a (111) substrate. The ratio of phosphorus atoms to carbon atoms in the gas which is used as a raw material, however, is at a level of approximately several tens of ppm to several thousands of ppm at the highest. This is because it was firmly believed that increase in the amount of n type atoms added to be harmful to the crystallinity of the fabricated n type diamond semiconductor single crystal film.

For example, in preparing p type diamond semiconductors, diborane B₂H₆ is used as an acceptor, but also it has been carried out with a ratio B/C of diborane to CH₄ of approximately several tens of ppm to several thousands of ppm. Though there are rare examples of experiments being conducted with a concentration of as high as 2000 ppm (Non-patent Document 3), the ratio in these is 0.2% at the highest. The crystallinity of diamond becomes poor when the concentration is further increased.

The n type (100) oriented single crystal diamond semiconductor, in particular, can show properties that provision of an enlarged area and flattening through polishing are relatively easy and the interface state density is low, and thus the (100) oriented single crystal diamond films are thus suitable for devices and have high utility value. However, n type conduction on (100) oriented diamond could not be attained substantially.

-   Non-patent Document 1: S. Koizumi et al., Appl. Phys. Lett., 71,     1065 (1997) -   Non-patent Document 2: S. Koizumi et al., Diamond and Related     Materials, 9, 935 (2000) -   Non-patent Document 3: K. Ushizawa et al., Diamond and Related     Materials, 7, 1719 (1998) -   Non-patent Document 4: M. Nesladek, Semicond. Sci. Technol., 20, R19     (2005)

DISCLOSURE OF INVENTION Problems that the Invention is to Solve

The present inventors diligently continued research in order to provide a film of an n type (100) oriented single crystal diamond semiconductor, as well as a method for manufacturing the film of an n type (100) oriented single crystal diamond semiconductor, and as a result, developed a film of an n type (100) oriented single crystal diamond semiconductor, as well as a manufacturing method for the same. The present inventors used the phosphorus vapor in a concentration at a level which deviates from that of common knowledge for doping, and thus, solved the problem. That is to say, while the weight ratio of phosphorus atoms to carbon atoms in the vapor phase for epitaxial growth was usually the order of the ppm, here it is the order of percentage, and thus, it was found that the present invention could be achieved.

Means to Solve the Problem

The present inventors discovered that by the existence of an unthinkable amount in light of common knowledge, that is to say, a large amount of n type atoms (phosphorus atoms), in microwave plasma can solve the problems above described when diamond semiconductor is grown homoepitaxially using a plasma chemical vapor deposition method. The present invention provides a film of an n type (100) oriented single crystal diamond semiconductor doped with phosphorus atoms and a manufacturing method for the same.

That is to say, the present invention relates to a film of an n type (100) oriented single crystal diamond semiconductor doped with phosphorus atoms.

In addition, the present invention relates to a manufacturing method for a film of an n type (100) oriented single crystal diamond semiconductor, characterized in that (100) oriented diamond is epitaxially grown on a substrate of (100) oriented diamond, by means of chemical vapor deposition where there are supplied hydrogen, hydrocarbon and a phosphorus compound in the plasma vapor phase, wherein the ratio of phosphorus atoms to carbon atoms in the plasma vapor phase is no less than 0.1%, and the ratio of carbon atoms to hydrogen atoms is no less than 0.05%.

Furthermore, according to the present invention, the means of chemical vapor deposition may be one selected from among the methods represented by microwave CVD, filament CVD, DC plasma CVD and arc jet plasma CVD.

In addition, according to the present invention, a diamond substrate having an off angle of 0 degree to 10 degrees where the plane is inclined by 10 degrees from 0 in any direction from the (100) plane can be used as the diamond substrate.

Furthermore, according to the present invention, the weight ratio of phosphorus atoms to carbon atoms in the plasma vapor phase can be controlled, in order to control the properties of the semiconductor.

In addition, according to the present invention, the temperature on the surface of the substrate can be set to 800° C. to 1000° C.

EFFECTS OF THE INVENTION

There is produced an n type (100) oriented single crystal diamond semiconductor for which enlarging of area and flattening are easy in accordance with the manufacturing method for an n type single crystal diamond semiconductor film of the present invention, in comparison with (111) oriented single crystal diamond semiconductor. Thus the n type (100) oriented single crystal diamond semiconductor can be used for developing general devices, and thus, have an extremely large impact into the industry, as it can achieve development of devices.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing the claims a previous patent according to the prior art, as well as working examples and comparative examples thereof.

FIG. 2 is a graph showing the scope of claims of the present application, as well as working examples and comparative examples thereof.

FIG. 3 is a graph showing dependency of the concentration of the carrier on the temperature.

FIG. 4 is a graph showing dependency of the mobility on the temperature.

FIG. 5 is a graph showing profiles for respective elements in relation to the depth gained through SIMS analysis.

FIG. 6 is a graph showing the distribution in the concentration of phosphorus in relation to the depth in comparison with Examples 8 and 9 (with off angles).

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention provides a synthesizing method for (100) oriented diamond into which phosphorus is doped by the synthesizing method a phosphorus compound is added to a reaction gas in accordance with a microwave plasma method for synthesizing diamond using hydrogen and hydrocarbon as a raw material gas so that a specific composition is set for the reaction gas, and hydrogen that bonds to phosphorus is dissociated for a chemical vapor phase growth method represented by a microwave plasma CVD method, a DC plasma CVD method and the like, and a single crystal or polycrystal thin film of diamond including phosphorus atoms is epitaxially grown on a (100) oriented diamond substrate which has been placed in a reactive container and heated. In addition, according to the present invention, the ratio of phosphorus atoms to carbon atoms in the vapor phase is controlled, and thus, the properties of the semiconductor can be controlled.

Here, (100), (010) and (001) are referred to as Miller's indices, and are numeral values for determining the crystal plane. In diamond crystals, these three are equivalent.

Examples of substances which can be used as the hydrocarbon in the present invention include carbon dioxide, carbon monoxide, methane and the like.

Examples of gas including phosphorus atoms which can be used in the present invention include phosphine, trimethylphosphine, and the like.

Though the unit for synthesis used for controlling n type conduction in the present invention is a microwave plasma chemical vapor phase deposition (CVD) unit according to the prior art, and the unit is not limited to this. The same results can be expected when other types of equipment, such as equipment for microwave CVD, filament CVD, DC plasma CVD and arc jet plasma CVD, are used.

Though the vacuum container used in the present invention is operated under a pressure of approximately 10 Torr to 200 Torr, the pressure greatly depends on the unit, and is not limited to this. Though the temperature for reaction is approximately 600° C. to 1200° C., and a temperature ranging from 800° C. to 1000° C. is particularly preferable, the temperature also greatly depends on the reaction gas and the unit, and thus the present invention is not limited to this.

In the present invention, a (100) oriented diamond substrate or a substrate with an off angle of 0 degree to 10 degrees where the (100) plane is inclined by 0 degree to 10 degrees in any direction is used as the diamond substrate for epitaxially growing crystal. The minimum value of the off angle may be 0 degree, preferably 0.5 degree, and more preferably no less than 1.0 degree.

Though well known n type elements and a complex dopant, such as N+4Si or N+S, can be used as the n type element, it is generally preferable to use phosphorus atom.

FIG. 3 shows the results of examination of the dependency of the concentration of the carrier on the temperature for film of phosphorus doped n type (100) oriented single crystal diamond semiconductor which was obtained by the present inventors in the working example, in comparison with already known n type (111) oriented diamond doped with phosphorus.

EXAMPLE 1

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.2% of methane so that the ratio of phosphorus (P) to carbon (C) became 5% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 50 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 1.5 degrees (a diamond substrate where the plane direction is inclined by 1.5 degrees in any direction for the (100) plane), on the substrate at 900° C. The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 350 cm²/Vs and the concentration of the carrier was 3×10⁹ cm⁻³.

EXAMPLE 2

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.5% of methane so that the ratio of phosphorus (P) to carbon (C) became 7.5% and the resulting gas was introduced into a reaction chamber kept at a pressure for synthesis of 75 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 2.8 degrees, at 800° C. on the substrate. The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 47 cm²/Vs and the concentration of the carrier was 9×10⁹ cm⁻³.

EXAMPLE 3

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.4% of methane so that the ratio of phosphorus (P) to carbon (C) became 5% and the resulting gas was introduced into a reaction chamber kept at a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 0.5 degrees at 900° C. of the substrate. The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 230 cm²/Vs and the concentration of the carrier was 5×10 ⁹ cm⁻³.

EXAMPLE 4

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.5% of methane so as to set of phosphorus (P) to carbon (C) to 2% and the resulting gas was introduced into a reaction chamber kept at a pressure for synthesis of 50 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 5.8 degrees, at 1000° C. on the substrate. The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 340 cm²/Vs and the concentration of the carrier was 9×10⁹cm⁻³.

EXAMPLE 5

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 1.0% of methane so as to set the ratio of phosphorus (P) to carbon (C) to 1% and the resulting gas was introduced into a reaction chamber kept at a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single. crystal diamond having an off angle of 3.4 degrees, at 800° C. on the substrate. The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 90 cm²/Vs and the concentration of the carrier was 5×10⁹ cm⁻³.

n type diamond semiconductor single crystal films having working examples (100) plane that was substantiated by are designated as ∘ in FIG. 2, can be attained. Meanwhile, it is described that comparative examples designated as × cannot attain films on the (100) plane.

Further, specific working examples according to the present invention are shown below.

EXAMPLE 6

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.4% of methane so that the ratio of phosphorus (P) to carbon (C) became 63% and the resulting gas was introduced into a reaction chamber kept at a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 1.6 degrees, at 900° C. on the substrate.

The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 18 cm²N/V and the concentration of the carrier was 1.5×10¹⁰ cm⁻³.

EXAMPLE 7

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.2% of methane so that the ratio of phosphorus (P) to carbon (C) became 40% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 1.0 degrees, at 900° C. on the substrate. The film was confirmed to have n type properties at room temperature by measuring the Hall effect, and the mobility thereof was 5 cm²/Vs and the concentration of the carrier was 1.2×10¹¹ cm⁻³.

Furthermore, a working example where the steepness in the distribution of the concentration of phosphorus in relation to the depth increased is shown below.

EXAMPLE 8

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.4% of methane so that the ratio of phosphorus (P) to carbon (C) became 5% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 2.0 degrees, at 900° C. on the substrate.

The film was confirmed to have n type properties at room temperature by measuring the Hall effect. The distribution in the concentration of phosphorus in relation to the depth at the time was measured through SIMS.

EXAMPLE 9

In accordance with a microwave plasma chemical vapor phase synthesizing method, phosphine was added to hydrogen containing 0.4% of methane so that the ratio of phosphorus (P) to carbon (C) became 5% and the resulting gas was introduced into a reaction chamber kept at a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 0.5 degrees, at 900° C. on the substrate.

The film was confirmed to have n type properties at room temperature through measurement using the Hall effect. The distribution in the concentration of phosphorus in relation to the depth is shown in FIG. 6, compared with the results of Example 8.

It was found that a suitable off angle for making the gradient in the concentration steep is no less than 1.0 degrees.

Phosphorus doped diamond was grown using a microwave plasma chemical vapor phase deposition unit, and the properties of the semiconductor were by measuring using the Hall effect, as shown in FIG. 4, and furthermore, the concentration of phosphorus was found through SIMS element analysis, as shown in FIG. 5, and thus, it was confirmed that phosphorus was doped without failure and control of n type conduction was possible.

The efficiency for taking in an n type dopant (phosphorus atoms) was different by no less than 100 between the (111) plane and the (100) plane. Under these circumstances, phosphorus is not taken in, even when doping is carried out in a range following conventional common knowledge, and n type conduction cannot be controlled. Meanwhile, the efficiency of doping depends on the rate of growth of diamond in such a manner that the efficiency for take-in increases as the rate increases. In this case, however, many defects are caused, or even if phosphorus is taken in, there is compensation, and thus, n type conduction is not exhibited.

The problem can be solved using a technology for effectively taking in phosphorus while suppressing the rate of growth (suppressing the amount of defects), as clarified in this specification.

FIG. 3 shows the results of measurement of the Hall effect of the n type (100) oriented single crystal diamond semiconductor gained in the working examples.

In contrast to these examples, n type properties could not be confirmed when the atomic ratio was in a range commonly known for conventional doping, as shown in the following comparative examples.

COMPARATIVE EXAMPLE 1

Phosphine was added to hydrogen containing 0.05% of methane so that the ratio of phosphorus (P) to carbon (C) became 0.001% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 25 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 1.3 degrees, at 800° C. on the substrate. No good epitaxial film having a (100) plane was formed, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

COMPARATIVE EXAMPLE 2

Phosphine was added to hydrogen containing 0.05% of methane so that the ratio of phosphorus (P) to carbon (C) became 0.01% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 100 Torr, and a diamond film were formed on the (100) oriented single crystal diamond having an off angle of 0.9 degrees and formed on the (111) plane of single crystal diamond having an off angle of 1.0 degrees, respectively, at 900° C. on the substrate. Though the n type properties of the gained film could be confirmed on the (111) surface at room temperature by measuring the Hall effect, and the mobility 50 cm²/Vs and the concentration of the carrier was 1.0×10¹¹ cm⁻³, no good epitaxial film having a (100) plane was formed, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

COMPARATIVE EXAMPLE 3

Phosphine was added to hydrogen containing 0.1% of methane so that the ratio of phosphorus (P) to carbon (C) became 0.03% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 50 Torr, and a diamond film were formed on the (100) oriented single crystal diamond having an off angle of 3.0 degrees and formed on the (111) oriented single crystal diamond having an off angle of 0.5 degrees, respectively, at 900° C. on the substrate. Though the n type properties of the gained film could be confirmed on the (111) plane at room temperature by measuring the Hall effect, and the mobility 45 cm²/Vs and the concentration of the carrier was 1.2×10¹¹ cm⁻³, no good epitaxial film having a (100) plane was formed, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

COMPARATIVE EXAMPLE 4

Phosphine was added to hydrogen containing 1% of methane so that the ratio of phosphorus (P) to carbon (C) became 0.1% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 75 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 1.6 degrees, at 850° C. on the substrate. No good epitaxial film having a (100) plane was formed, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

COMPARATIVE EXAMPLE 5

Phosphine was added to hydrogen containing 0.5% of methane so that the ratio of phosphorus (P) to carbon (C) became 0.01% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 75 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 1.6 degrees, at 850° C. on the substrate. No good epitaxial film having a (100) plane was obtained, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

COMPARATIVE EXAMPLE 6

Phosphine was added to hydrogen containing 0.05% of methane so that the ratio of phosphorus (P) to carbon (C) became 0.1% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 85 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 2.7 degrees, at 900° C. on the substrate. No good epitaxial film having a (100) plane was obtained, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

COMPARATIVE EXAMPLE 7

Phosphine was added to hydrogen containing 0.05% of methane so that the ratio of phosphorus (P) to carbon (C) became 5% and the resulting gas was introduced into a reaction chamber having a pressure for synthesis of 80 Torr, and a diamond film was formed on the (100) oriented single crystal diamond having an off angle of 2.7 degrees, at 900° C. on the substrate. No good epitaxial film having a (100) plane was gained, and n type conduction could not be confirmed according to the results of measurement using the Hall effect.

INDUSTRIAL APPLICABILITY

In the manufacturing method of an n type single crystal diamond semiconductor film of the present invention, production of an enlarged area and flattening are easy and the interface state density can be made low in the n type (100) oriented single crystal diamond semiconductor, in comparison with (111) oriented single crystal diamond semiconductor. The (100) oriented single diamond crystal film, can be used for developing general semiconductor devices, and thus, has an extremely large impact in the industry, as they can be utilized for every type of development of devices. As examples of devices, the n type (100) oriented single crystal diamond according to the present invention can be applied to such electric devices as ultraviolet light emitting devices, electron emission sources, high frequency transistors, high power transistors, X ray and particle ray sensors, and X ray and particle position sensors. 

1. An n type (100) oriented single crystal diamond semiconductor film doped with phosphorus atoms.
 2. A method of producing an n type (100) oriented single crystal diamond semiconductor film, comprising growing on a diamond substrate epitaxially under such conditions that; the substrate is (100) oriented diamond, a means of chemical vapor phase deposition provides hydrogen, hydrocarbon and a phosphorus compound in the plasma vapor phase, the ratio of phosphorus atoms to carbon atoms in the plasma vapor phase is no less than 0.1%, and the ratio of carbon atoms to hydrogen atoms is no less than 0.05%.
 3. The method of producing an n type (100) oriented single crystal diamond semiconductor film according to claim 2, wherein the means of chemical vapor phase deposition is selected from among the methods represented by microwave CVD, filament CVD, DC plasma CVD and arc jet plasma CVD.
 4. The method of producing an n type (100) oriented single crystal diamond semiconductor film according to claim 2, wherein the diamond substrate having an off angle of 0 degree to 10 where the plane oriented is inclined by 10 degrees from 0 to any direction from (100)plane can be used as the diamond subrate.
 5. The method of producing an n type (100) oriented single crystal diamond semiconductor film according to any one of the claims 2 to 4, wherein the weight ratio of phosphorus atoms to carbon atoms in the plasma vapor phase can be controlled, so that the properties of the semiconductor can be controlled.
 6. The method of the producing an n type (100) oriented single crystal diamond semiconductor film according to claim 2, wherein the temperature on the surface of the substrate can be set to 800° C. to 1000° C. 